Method and apparatus for the comminution of wood

ABSTRACT

Pointed wood particles for use in the production of pressed board or in the paper or cellulose industries are made by shaving a wood body in the direction generally transverse to a major dimension thereof and inclined at an acute angle to the grain to produce shavings which are thereafter broken up to form the particles. The apparatus comprises a drum whose blades along the exterior are provided with slots through which the shavings pass into the interior of the drum and are conveyed by a worm, belt or flight conveyor within the latter.

United States Patent Schafer et al. Nov. 20, 1973 [54] METHOD AND APPARATUS FOR THE 2,776,687 1/1957 Clark 144 172 x COMMINUTION 0 WOOD 2,849,038 8/1958 Clark 241/280 X 3,304,970 2/1967 Altosaar 144/172 X Inventors: Karl Schafer, Neu-Bamberg; Peter Voelskow, Bad Kreuznach, both of Germany G. Siempelkamp & Co., Krefeld, Germany Filed: May 14, 1971 Appl. N0.: 143,497

Assignee:

US. Cl 241/28, 241/280, 144/172 Int. Cl B27! 11/00 Field of Search 241/28, 91, 92, 93, 241/277, 278 R, 280, 144/172 References Cited UNITED STATES PATENTS 8/1959 Schubert 144/172 Primary Examiner-Granville Y. Custer, Jr. Attorney-Karl F. Ross [57] ABSTRACT Pointed wood particles for use in the production of pressed board or in the paper or cellulose industries are made by shaving a wood body in the direction generally transverse to a major dimension thereof and inclined at an acute angle to the grain to produce shavings which are thereafter broken up to form the particles. The apparatus comprises a drum whose blades along the exterior are provided with slots through which the shavings pass into the interior of the drum and are conveyed by a worm, belt or flight conveyor within the latter.

14 Claims, 12 Drawing Figures FIG.2

FIG.

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METHOD AND APPARATUS FOR THE COMMINUTION OF WOOD FIELD OF THE INVENTION Our present invention relates to a method of and an apparatus for the comminution of wood and, more particularly, to a method of and an apparatus for producing wood particles, especially for use in pressed board or in the paper or cellulose trades.

BACKGROUND OF THE INVENTION It is a common requirement for various industrial processes that wood particles be supplied from a source of waste material or as a raw material from wood bodies such as tree trunks and the like which are harvested especially for this purpose.

For example, in the production of pressed board, cellulosic fibers or wood particles (e.g., sawdust, chips, shavings or splinters) are generally required and may be milled or otherwise subdivided and can be graded or used in a wide particle-size range to form mats in the presence of binder materials which are intrinsic to the wood or are supplied from some external source. The fiber mat or mat of loosely coherent or noncoherent particles may be conveyed upon a tray or upon a conveyor surface to a stacking rack and introduced between platens of a multiplaten press or pressed individually in a roller press or a platen press. Compression under heat and pressure results in a pressed board, also known as particle board or fiberboard. Such pressed board may have a core layer of particles of one size, sandwiched between or flanked by cover layers or outer layers of particles of a different size (generally finer than the core layer) to provide a less porous surface of greater esthetic value and improved texture.

Pressed board may be made in a wide variety of thicknesses and sizes, depending upon the requirements and various parameters and in a variety of densities ranging from a highly cellular, light-weight and porous structure of considerable volume for insulation, to a highly dense, rigid and strong structure of considerable value in construction. The critical parameters, aside from the nature of the wood particles, the particle size and the particle size and the particle configuration, are of course the degree of compression, the quantity, character and nature of any thermosetting resins used as binders, the moisture content of the particles and the processing of the fiberboard.

We may also mention that wood particles are useful in other technologies as well, namely in the production of paper or cellulosic products, e.g., regenerated cellulose. For example, in the production of paper and cellulose, wood particles are digested to break down the natural resins which hold the cellulosic fibers together, thereby forming fibrous masses consisting primarily of cellulose. Thus, it is evident that the comminution of wood to produce wood particles is of considerable interest.

In all of the above industries it is desirable to maintain the wood particles in a form which contributes to the characteristics of the end product and, therefore, provides some sort of directionality which may be employed to increase the strength of the product. Consequently, in the paper and cellulose production industries, the wood particles preferably are elongated so as to yield fibers of a length sufficient to the end result.

It is known, more specifically, in connection with the production of pressed board to derive the wood particles as a waste product from some other manufacturing process involving wood. This waste product may be chips, shavings and sawdust derived from furniture plants, lumber mills and the like. In addition, it is known to comminute wood as a raw material especially for the production of wood-fiber board.

In prior-art systems of the latter type, a log or other massive wood body having a grain orientation generally in the longitudinal direction may be shaved or chopped into thin leaf-like elements having a thickness of 0.2 to 0.6mm. Chips of a thickness of 0.4mm (approximately) are commonly used for the core or central layer of multilayer pressed board while chips of a thickness of 0.2mm (approximately) may be used for the cover, facing or outer layers of the wood-fiber board. The comminuting process is, however, relatively expensive because, firstly, large wood bodies must be manipulated 0 because wear of the cutting blades is relatively high and because considerable energy is necessary to drive the system. In practice, energy costs of 20 to 40 kWh/metric ton of comminuted wood are not unusual. The blades have a useful life on the average of 2 to 4 hours in comminuting machines which have a capacity of 6 to 8 metric tons of wood particles in this period, when small particles are made, and a useful life of 20 metric tons when particles are produced for the core layer of the pressed board. Not only are the costs high for the sharpening, adjustment and replacement of the worn blades, but the downtime of the apparatus is considerable if a large number of blades is provided.

It has also been suggested to substitute for the shaving process described above, a wood-chopping process whereby the wood is comminuted by the chisel-like impact of massive blades thereagainst. Such woodchopping characterizes the production of wood particles in the paper and cellulose industries. Woodchopping machines may have an output of 20 to 60 metric tons/hour. However, the chips produced by the process frequently must be further comminuted by, for example, blade-ring comminuters which have the disadvantages discussed above of high-blade wear, energy cost and downtime or replacement cost. When the two comminution steps are taken together, they have even greater disadvantages than the shaving system mentioned earlier. Finally, we may mention that the latter system frequently produces wood particles whose characteristics are poorer than those of the shaving system mentioned earlier for many purposes.

For example, a chopping machine of conventional construction may operate with energy cost of 20 kWh/metric ton of comminuted wood, to which must be added the operating costs of the further comminution stage. To limit these costs, it has been suggested to avoid the further mechanical comminution stage and to introduce the wood chips directly into a refining apparatus in which pressure, heat and the like are used to break down the wood structure and form fiber bundles therefrom which may be used in the usual manner in the paper and cellulose industries and which may be dry-pressed to produce fiberboard. Even this system has significant disadvantages since the energy costs of operating the refining devices with wood chips derived directly from the chopping apparatus is higher than mechanical comminution. When the refiner is operated in a wet mode, excessive softening of the chips occurs to the extent that the product may be treated in a socalled defibrator; the product, however, is excessively fluffy for use in the dry-pressing of fiberboard. As a consequence, the dry process for producing fiberboard can be carried out only with hard fibers and only to yield thin sheets or plates.

As far as the prior-art comminuting devices are concerned, we also must make mention of the fact that, for the production of paper and in the cellulose industry, it is desirable that the wood particles which are used have an acute-angle character, meaning that the grain structure and the major longitudinal dimension of the particle should lie at an angle to the end face. It has been proposed to produce shaving and chopping machines in which a plurality of blades are angularly spaced about a drum and the block, body dr log of wood is fed to the latter so that the blades chip away and split particles from the wood. These particles are generally nonuniform and have undesirable characteristics for many purposes in the paper industry. To obtain greater uniformity and the aforementioned acute angles, it is not uncommon for a central blade to be fed transversely to the grain and to be flanked by two acute-angle blades whose cuts define the end phases. Such systems produce deformation-free particles of high quality but the machine operation is disadvantageous since complicated shaving processes at considerable expense in time and money are required to prepare the many blade surfaces.

Drum-type choppers whose blades lie in helical patterns along a conical drum have also been provided. The particles are produced with the desired inclination, i.e., with a cut intersecting the grain direction at an acute angle, although the drum-type chopper offers difficulty with respect to replacement, sharpening and readjustment of the blades. A further significant disadvantage of these conventional drum-type choppers is that the wood, before it is fed to the machine, must be cut to the length of the machine or drum.

OBJECTS OF THE INVENTION It is an important object of the present invention to provide a method of and an apparatus for the comminution of wood whereby high-quality particles may be obtained at relatively low cost and without any of the disadvantages of the systems described earlier.

It is another object of the invention to provide an improved method of producing wood particles, especially for use in the production of pressed board, whereby the particles have improved characteristics and uniformity and whereby the method of production is of lower cost than prior-art systems.

Still another object of the invention is the provision of a wood-comminuting apparatus in which the cutting members can be conveniently and readily replaced, sharpened or removed, in which higher quality wood particles can be provided, and in which the energy cost is reduced.

Yet a further object of this invention is the provision of a wood-comminuting apparatus for producing acuteangle wood particles which are especially desirable in the paper and cellulose industries.

SUMMARY OF THE INVENTION These objects and others which will become apparent hereinafter are attained, in accordance with the present invention which in one of its vital aspects provides a generally flat particles. Finally, these particles are drymilled to produce chips and fiber bundles with pointed ends.

The formation of the shavings is carried out generally in the manner of veneer production except that the wood body is fed at an acute angle to a drum-type shaving apparatus so that the blades sever the shavings in the direction generally transverse to the grain orientation. Cutting in this manner requires small amounts of energy. The subsequent crumbling or breakdown of the shavings during the milling step likewise requires little energy because the shavings naturally tend to crumble or separate parallel to the wood fibers. It is possible in this fashion to break down the generally flat pieces broken initially from the shavings into fine fiber bundles which are used for the cover layers or facing layers of the fiber wood and into relatively coarse fiber bundles or chips suitable for use as the core layer of the pressed board.

According to another feature of this aspect of the invention, the flat pieces broken from the chips are subjected under atmospheric pressure to steam (steaming) to produce fiber bundles and particles especially useful in the subsequent pressing to produce fiberboard. We have found that cutting speeds (i.e., the rate at which the shavings are formed) can be about 6 meters per second for optimum comminution. The cutting drum of the present invention thus can operate at speeds substantially slower than the 40 meters per second of conventional chopping machines, thereby reducing the centrifugal forces which might otherwise retain the wood particles against the inner surface of the drum.

According to a further aspect of the invention, the apparatus comprises, in addition to the cutting drum, which is generally cylindrical and is provided with an array of outwardly projecting angularly equispaced blades, a conveyor worm within the drum which is provided with slots through which the shavings pass, the conveyor drum serving both to advance the particles from the apparatus and as a milling device for further comminuting the shavings. The shaving blades lie along secants of the drum and project only slightly therebeyond, while extending axially along the drum periphery and are disposed immediately adjacent the slots which also can open into the drum along secants thereof.

A feed means is provided for urging the log or body of wood toward the drum at the aforementioned acute angle, preferably 9 to 15 with a generatrix of the drum or the drum axis. At this angle, the shavings pass into the drum and break up upon contact of the shavings with the worm so that the relatively rotating members need overcome only the forces of adhesion between the fibers which are never out transversely to the grain. The worm extends coaxially within the drum and may have its generatrix reaching substantially to the inner wall of the drum. Moreover, the worm may be rotated in a direction opposite that of the drum so that the drum and the worm are counterrotating. Since the lengths of the shavings are independent of the spacing between the blades or slots but is a function of the frequency of contact of the turns of the worms with the shavings (i.e., the frequency with which a turn of the worm sweeps across each slot) it is advantageous to provide the worm of the multiple-thread type.

According to another feature of the invention, the hollow drum, which rotates about a horizontal axis provides at its discharge side a storage cover or member in which the fiber bundles or particles, produced by the milling effect of the counterrotating drum and worm can accumulate.

Alternatively, the inner wall of the drum may be provided with entraining members or scoops located adjacent the slots and serving both as guides and as comminuting members which cooperate with interleaved rake-like formations fixed in the interior of the drum to break up the shavings.

The discharge device may extend axially through the drum and may be provided in a coaxial but stationary trough whose opening extends along the stripping teeth of the rakes to catch the comminuted shavings.

The lengths of the particles is here determined by the transverse spacing of the entraining scoops and the cooperating teeth so that a narrower spacing results in shorter particles.

A plurality of such strippers may thus be provided one behind the other and may have means for adjusting the relative spacing of the strippers.

DESCRIPTION OF THE DRAWING The above and other objects, features and advantages of the present invention will become more readily apparent from the following description, reference being made to the accompanying drawing in which:

FIG. 1 is an axial cross-sectional view through a wood-comminuting drum according to the present invention;

FIG. 2 is a transverse cross-sectional view of the drum of FIG. 1;

FIG. 3 is an axial cross-sectional view, similar to FIG. 1, illustrating another embodiment of the invention;

FIG. 4 is a transverse cross-sectional view through the drum of FIG. 3;

FIG. 5 is a view similar to FIG. 4 of still another embodiment of the invention wherein conveyor belts serve to move the comminuted product;

FIG. 6 is a view similar to FIG. 4 of an embodiment in which a scraper conveyor serves as an additional comminuting device;

FIG. 7 is a diagrammatic view illustrating the formation of a wood particle according to the present inven' tion;

FIG. 8 is a diagram illustrating how the body of wood is fed to the drum;

FIG. 9 is a diagram illustrating a feature of the invention;

FIG. 10 is a diagrammatic perspective view showing the wood shaving prior to initial breakup;

FIG. 11 shows how the shaving is initially broken; and

FIG. 12 is a diagram illustrating the comminuted product.

SPECIFIC DESCRIPTION Referring first to FIGS. 9 and 11, it will be seen that,

in general, the wood body is fed at an acute angle to the blade drum of which one blade is shown at 101 in FIG. 9. While, in general, the blades are carried by a drum (FIGS. 1 8) rotatable about a horizontal axis and the wood is fed to the drum generally laterally (FIG. 8), the method aspects of the present invention may best be understood by recognizing that each blade 101 sweeps the log 100 in an are represented by the arrow 102 and, because of the acute angle, moves generally transversely to the grain orientation 103 but slices the wood substantially parallel to the grain to form the shaving 104.

The term substantially parallel is used herein to refer to a shaving of the wood at an acute angle of 7 20 to the grain orientation, preferably 9 15 and, even more advantageously, 12 15. The shaving 104, as best seen in FIG. 10, thus has its grain orientation 105 running at an acute angle B of about 12 to the surface 106 or 107, one of which is formed by the preceding cut while the other is formed by the current cut. The shaving preferably has a thickness (FIG. 10) which ranges between 1 and 5 mm and is about 2 mm as represented in the drawing in approximately S-times enlargement. The preferred thickness is about 2 3 After the shaving 104 is removed from the wood body, it may be preliminarily broken up as shown in FIG. 11 into two flat chips (small pieces) 108 and 109, each of which has a grain orientation 110 and 111 running at the acute angle B to the upper and lower surfaces 112 and 113. Since the subsequent breakdown of the basic shaving takes place parallel to the grain orientations 105, 110, 111, the separation between the chips 108 and 109 takes place at 114 along the grain and re quires overcoming any of the adhesion forces between the grain planes. This breakdown of the shaving occurs almost naturally as the shaving is fed in the direction of arrow 115 and encounters a milling member moving in the direction 116, i.e., intercepting the leading edge of the shaving. Subsequently, the chips 108 and 109 are broken down by aftermilling in a similar manner into wood particles 117 having pointed ends 118, 119 resulting from the angle at which the log was originally fed to the drum.

Surprisingly, the present technique producing comminuted wood has been found to be highly advantageous for the production of pressed board from the particles 117, especially where these particles are used in the core layer of the pressed board. Because of the pointed ends of the particles, the resistance of the board to transverse stress is greater while the swelling of the board by absorption of moisture is reduced. The structure of the core layer is substantially more dense and closer than with other wood-chip board and the resistance of the board to breakdown when nails and screws are driven into it is increased. In addition, blade replacement, sharpening and adjustment costs are lowered while the energy required for comminuting the wood is reduced. Prior to milling the pieces of wood are subjected to steam treatment at atmospheric pressure.

In FIGS. 1 8, we have shown the system for comminuting wood in several embodiments and in somewhat greater detail. The machine of FIG. 1, for example, comprises a horizontal drum 1 which coaxially receives a worm 2 having a shaft 3 joumaled in bearings 4 and 5 at opposite ends of the drum. The worm 2 is of the multiple-thread type and in the embodiment shown as a double-pitch thread whose turns are represented at 20 and 2b. The worm 2 is driven by an electric motor via a belt drive connected to a pulley 6 keyed at 6a to the end 3a of shaft 3 projecting outwardly beyond the bearing 5. The turns, threads or lands of worm 2 reach to the inner wall 18a of the cylindrical shell 18 of the drum and sweep across the slots 16 formed therein to guide the shaving 17 into the drum interior. The outer periphery of the worm 2 is thus defined by a generatrix which coincides with the generatrix of the inner cylindrical wall of the drum.

The hollow drum 1 is provided at one end with a bearing cover or plate 7 into which the cylindrical shell is fitted, and having a cylindrical base 7a journaled in the bearing 13 of a support 13a. A stub 8 of the base 7a projects axially beyond the bearing 13 and is keyed at 8a to a pulley 9 connected to a beld drive for the drum. In this embodiment, the worm is rotated in one sense while the drum is rotated in the other. In FIG. 2, for example, a woodbody is shown at 120 to underlie the drum 1 18 which is rotated in the direction of arrow 121 (clockwise) while the worm 2 is rotated in the opposite direction (arrow 122) or counterclockwise.

The bearing holder 10 at the other end of the drum receives a bearing 5 and is provided with a spider 11 through which the comminuted wood can be discharged. A bearing 14 supports the outer periphery of the drum 118 adjacent this end in a support 14a. As best seen in FIG. 2, the outer periphery of the drum is formed with blades 15 in angularly equispacedl relation, the blades 15 projecting slightly beyond the outer drum surface and lying along respective secants of the cylinder. Each blade 15 extends axially along the drum and is disposed adjacent the respective slot 16 through which the shaving 17 may pass.

In operation, a feed device, represented at 46 in FIG. 8, serves to advance the body of wood 100 against the drum 1 in the direction of arrow 123 and includes an angle a of 9 15 with a generatrix of the drum, the drum being rotated in the counterclockwise sense as represented by the arrow 121 also illustrated in FIG. 8. The speed of advance of the log and the peripheral speed of the drum are such that shavings are produced at a rate of approximately 6 meters per second.

As seen in FIG. 2, shavings 17 pass through the slots 16 into the interior of the drum where they are broken up by the counterrotating worm 2 and transformed into the pieces 108, 109 and then into particles such as those shown at 117 in FIGS. 11 and 12. The particles are advanced by the worm to the spider 10 where they fall between the arms of the spider and into the trough 12 which may be provided with a belt, flight or scraper conveyor as described at pages 7 6 ff of PERRY S CHEMICAL ENGINEERS HANDBOOK, McGraw- Hill Book Company, N.Y., [963.

As we have noted earlier, the feed of the wood body to the drum at the acute angle and the shaving motion of the blades transverse to the wood fibers represented at 39 in FIG. 7 produces the shavings 17 (FIG. 2) which are then broken up into small chips or particles 38. The slots of the drum are represented at 33 (analogous to slots 16). Since the fibers 39 run parallel to the original direction of feed, the ends 40 of the particles 38 are pointed or are at acute angles to the length of the parti' cle. Member 27 represents an entrainer as described in connection with FIGS. 3 and 4, infra.

In FIGS. 3 and 4, we have shown a comminuting device in accordance with another embodiment of the in vention. In this case, the drum is journaled in bearings 19 and 24 in the manner previously described but is n'gidly connected along its interior with a coaxially arranged worm 21 whose shaft 22 is supported in a wormtrough bearing 23. The other end of this shaft is mounted in a bearing 20. The worm 21 is surrounded except along its upper side with the worm trough 25 fixed at 26 to a stationary part of the system whereby both the worm and the drum rotate relative to this trough. The drum is here also provided with blades and slots as shown at 15 and 16 in FIGS. 1 and 2, each slot being provided along the inner surface of the drum with a guide scoop or entrainer 27 (see FIGS. 3 and 4). Each of the entrainers has a plurality of axially spaced fingers as shown at the bottom in FIG. 3. The entrainers 27 cooperate with strippers 28 fitted to the trough 25 and forming rake-like members interleaved with the teeth of entrainers 27. The strippers 28 are relatively adjustable or shiftable. To this end, the strippers 28 are provided with slots 33 through which entrainers 27 pass.

The upper portion of the trough 25 is open along its entire length ahead of the stripper 28 to define an inlet 29 into which the broken shavings pass. The drum 1 and the worm 21 are driven by a pulley 34 from a belt arrangement not shown and connected via the bearing cover 7 as previously described to the drum.

In this embodiment as well, the body of wood to be comminuted is fed at an acute angle against the rotating drum and is shaved to produce the foils which are broken up longitudinally as the members 27 pass the stripper 28. In addition, the relative movement of the drum and the stripper breaks down the shaving as described in connection with FIGS. 11 and 12 to produce the particles 117. The particles fall into the trough 25 and are entrained by the worm 21 out of the machine through the discharge end 35 of this trough. The partis are l aware th es yey an ss e t In FIG. 5, we have shown a modification of the system of FIG. 4 wherein, in place of the screw-type conveyor of this latter Figure, a conveyor belt 41 is provided for carrying away the particles. In the arrangement of FIG. 6, a scraper-type conveyor is provided at 42 above a perforated plate 43 or grate which cooperates with the scraper flights to further comminute the particles. An underlying trough 45 then receives the particles which can be removed, e.g., by a belt conveyor. Belt and flight conveyors of the type used in the systems of FIGS. 5 and 6 are described in the aforementioned publication.

As explained in PERRYS CHEMICAL ENGI- NEERS HANDBOOK, the belt conveyor of FIG. 5 carries the mass of particles 41a upon a belt 41 received in an upwardly open trough 41b, the belt riding upon a support surface 410. The return pass 41d of the belt is supported on a lower surface 41e. The belt may pass over rollers as shown at its opposite ends and can be driven in a manner well known in the art.

In FIG. 6 the flight conveyor has its upper base 44 displaceable by chains along the perforated surface 43 within a trough formed by walls 42a and 42b, to carry the particles 420 in the axial direction. The system operates otherwise in a manner similar to that of FIG. 4 and the cooperation of the flights with the perforated surface fsurther comminutes the particles.

We claim: 7 H A; 7 swims l. A method of producing wood particles, comprising the steps of shaving a body of wood having a predetermined grain orientation in a direction transverse to the grain orientation but intersecting same at an acute angle of substantially 7 to 20 to produce shavings having a thickness of 2 to 3 mm and having a grain extending at an angle of substantially 7 to 20 to the cut surfaces of the shaving; and breaking said shavings into particles along the grain of the shavings whereby said particles have acute-angled ends by feeding said shavings in the direction of the grain thereof against a transversely moving surface.

2. The method defined in claim 2 wherein in the step of breaking said shavings into particles, said shavings are first broken into smaller pieces and said pieces are thereafter milled to produce said particles.

3. The method defined in claim 2 wherein prior to milling of said pieces and after the shavings are broken into smaller pieces, said pieces are treated with steam at atmospheric pressure 4. The method defined in claim 1 wherein said shavings are removed from said body at a speed of 6 meters per second.

5. An apparatus for comminuting wood, comprising a drum rotatable about an axis, a plurality of angularly spaced axially extending shaving blades mounted in said drum and projecting outwardly thereof for cutting respective shavings from a wood body urged against said drum, said drum being formed with respective slots adjacent each of said blades and passing the respective shavings into the interior thereof, means for feeding a wood body at an acute angle of substantially 9 to 20 to the drum axis against the periphery of said drum, and means within said drum for comminuting said shavings and conveying the wood particles resulting from comminution of said shavings out of said drum.

6. The apparatus defined in claim wherein the lastmentioned means includes a conveyor worm rotatable within said drum.

7. The apparatus defined in claim 6 wherein said conveyor drum has at least one thread closely approaching an inner wall of said drum, further comprising means for driving said drum and said worm in opposite senses whereby said worm engages said shavings as they pass through said slots to comminute said shavings.

8. The apparatus defined in claim 6, further comprising a trough receiving said worm, said worm being coupled with said drum for rotating jointly therewith, entraining fingers formed on the interior of said drum for carrying said shavings therewith, and a stripper interleaved with said fingers and mounted on said trough for cooperating with said fingers to break up said shavings and deposite same in said trough.

9. The apparatus defined in claim 5 wherein the lastmentioned means includes a trough extending in said drum and having an upwardly open portion, entraining means mounted along the interior of said drum for entraining said shavings therewith, a stripper mounted on said trough and interleaved with said entraining means for comminuting said shavings to produce wood particles and depositing same in said trough.

10. The apparatus defined in claim 9 wherein a plurality of such strippers is provided.

11. The apparatus defined in claim 9, further comprising a conveyor worm rotatable in said trough for advancing said particles out of the latter.

12. The apparatus defined in claim 9, further comprising a belt conveyor in said trough for advancing said particles out of the latter.

13. The apparatus defined in claim 9, further comprising a flight conveyor in said trough for advancing said particles out of the latter.

14. The apparatus defined in claim 13, further comprising a perforated plate cooperating with the flights of said conveyor for further comminuting said particles. 

1. A method of producing wood particles, comprising the steps of shaving a body of wood having a predetermined grain orientation in a direction transverse to the grain orientation but intersecting same at an acute angle of substantially 7* to 20* to produce shavings having a thickness of 2 to 3 mm and having a grain extending at an angle of substantially 7* to 20* to the cut surfaces of the shaving; and breaking said shavings into particles along the grain of the shavings whereby said particles have acute-angled ends by feeding said shavings in the direction of the grain thereof against a transversely moving surface.
 2. The method defined in claim 2 wherein , in the step of breaking said shavings into particles, said shavings are first broken into smaller pieces and said pieces are thereafter milled to produce said particles.
 3. The method defined in claim 2 wherein prior to milling of said pieces and after the shavings are broken into smaller pieces, said pieces are treated with steam at atmospheric pressure .
 4. The method defined in claim 1 wherein said shavings are removed from said body at a speed of 6 meters per second.
 5. An apparatus for comminuting wood, comprising a drum rotatable about an axis, a plurality of angularly spaced axially extending shaving blades mounted in said drum and projecting outwardly thereof for cutting respective shavings from a wood body urged against said drum, said drum being formed with respective slots adjacent each of said blades and passing the respective shavings into the interior thereof, means for feeding a wood body at an acute angle of substantially 9* to 20* to the drum axis against the periphery of said drum, and means within said drum for comminuting said shavings and conveying the wood particles resulting from comminution of said shavings out of said drum.
 6. The apparatus defined in claim 5 wherein the last-mentioned means includes a conveyor worm rotatable within said drum.
 7. The apparatus defined in claim 6 wherein said conveyor drum has at least one thread closely approaching an inner wall of said drum, further comprising means for driving said drum and said worm in opposite senses whereby said worm engages said shavings as they pass through said slots to comminute said shavings.
 8. The apparatus defined in claim 6, further comprising a trough receiving said worm, said worm being coupled with said drum for rotating jointly therewith, entraining fingers formed on the interior of said drum for carrying said shavings therewith, and a stripper interleaved with said fingers and mounted on said trough for cooperating with said fingers to break up said shavings and deposite same in said trough.
 9. The apparatus defined in claim 5 wherein the last-mentioned means includes a trough extending in said drum and having an upwardly open portion, entraining means mounted along the interior of said drum for entraining said shavings therewith, a stripper mounted on said trough and interleaved with said entraining means for comminuting said shavings to produce wood particles and depositing same in said trough.
 10. The apparatus defined in claim 9 wherein a plurality of suCh strippers is provided.
 11. The apparatus defined in claim 9, further comprising a conveyor worm rotatable in said trough for advancing said particles out of the latter.
 12. The apparatus defined in claim 9, further comprising a belt conveyor in said trough for advancing said particles out of the latter.
 13. The apparatus defined in claim 9, further comprising a flight conveyor in said trough for advancing said particles out of the latter.
 14. The apparatus defined in claim 13, further comprising a perforated plate cooperating with the flights of said conveyor for further comminuting said particles. 